The core part of the UniPhier pinctrl driver needs to support a new
capability for upcoming UniPhier ARMv8 SoCs.  This sometimes happens
because pinctrl drivers include really SoC-specific stuff.

This commit intends to tidy up SoC-specific parameters of the existing
drivers before adding new ones.  Having flags would be better than
adding new members every time a new SoC-specific capability comes up.

At this time, there is one flag, UNIPHIER_PINCTRL_CAPS_DBGMUX_SEPARATE.
This capability (I'd say rather quirk) was added for PH1-Pro4 and
PH1-Pro5 as requirement from our customer.  For those SoCs, one pin-mux
setting is controlled by the combination of two separate registers; the
LSB bits at register offset (8 * N) and the MSB bits at (8 * N + 4).
Because it is impossible to update two separate registers atomically,
the LOAD_PINCTRL register should be set in order to make the pin-mux
settings really effective.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>